ERBB2 and breast cancer: As a member of the epidermal development factor receptor family of transmembrane receptors, the human epidermal growth factor receptor-2 (HER2) receptor tyrosine kinase exerts important effects on both growth and cancer.[2,3] Amplification and overexpression of the HER2 gene are present in 20% to 25% of human breast cancer and are associated with poor clinical results.[3,4] HER2 protein overexpression is measured by immunohistochemistry (IHC)-based test.